The Secret of the Vote
a detective story for lawyers
Robert Riemann with supervision of Stéphane Grumbach
The Voting Protocol shall provide legitimacy for the voting outcome.
-
secrecy of the ballot:
no coercion or ballot selling -
correctness:
final tally is sum of individual votes -
verifiability:
proof of the correctness -
voter convenience:
significant voter turnout - and many more...
Important Properties:
PhD Thesis
Decentralised Political Election Systems Based On Social Networks
- vote counting without trusted authority
- every voter participates in counting
- hierarchy: groups with intermediate tallies
Alice
Bob
Secrecy of the Ballot
Alice
Bob
Vote:
Vote:
exchange
No
?
192.158.2.1
121.201.76.12
What means secret?
What is knowledge?
information theory
Information after Shannon:
Example:
- Alice and Bob voted: tally contains Dagobert and Phantomias
- redundancy: if Alice’s vote is known, those of Bob as well
- H is maximal if probability
p(Alice voted for Phantomias) = 50%
Secrecy
All configurations are equally probable.
Example:
Alice voted with 50% probability for Phantomias and with 50% for Dagobert.
secrecy of
the ballot
The ballot for Dagobert has been filled with 50% probability by Alice or Bob.
secrecy of
the voter
=
Secrecy
If Alice voted for Phantomias with 70% probability, is this still secret?
If Alice and Bob voted both for Phantomias, there is no secret!
If Alice gives Bob a procuration, there is no secret!
Correctness
Ballots are counted by humans.
How do we deal with the uncertainty in the case of a very close voting outcome?
Example:
French municipal (Lescar, 2014) produced a tie with 2,670 votes
Image: Fickr/UNDP
Secrecy of Voting Today
- DNA fingerprint (invisible ink) on paper
- video surveillance (with smartphones)
- Big Data analysis based on Social networks
- (unconscious manipulation ahead of voting)
Technological progress weakens paper-based voting protocols.
Expectations on Specification
Legislation
- precise definition of secrecy
- description of required tolerance
Voting Legislation
in France
Le dispositif garantit que l’identité de l’électeur ne peut pas être mise en relation avec l’expression de son vote, à tout moment du processus de vote, y compris après le dépouillement.
à 100% ?
Voting Legislation
in France
Aucun décompte partiel n'a pu être effectué durant le scrutin.
sondage à la sortie des urnes?
Le bureau du vote
électronique vérifie que les listes d'émargement sont vierges et que l'urne électronique est vide.
avec les yeux ?
Voting Legislation
in France
[Le vote] fait l'objet d'un chiffrement dès son émission sur le terminal utilisé par l'électeur.
Qui peut déchiffrer ?
Affirmation du loi :
Les membres du bureau du vote électronique sont honettes.
Pourquoi ? Encore dans 20 ans ?